Got through the backtracking solution fine, mapped each digit to its letters and recursed through positions.
Start by clarifying the problem constraints (e.g., input length, empty input, digit '1' or '0') and then propose a backtracking solution that builds combinations digit by digit. Discuss the time complexity O(4^n * n) and space complexity O(n) for recursion, and mention potential optimizations like iterative BFS or pruning.
Pro tip: At Uber, interviewers value clean, production-ready code and awareness of edge cases. Write modular code with a helper function for backtracking, and explicitly handle empty input and invalid digits to show robustness.
Ask about input size, possible digits (e.g., 0,1), and expected output format. Confirm that the mapping is standard phone keypad and that order of combinations doesn't matter.
Propose a backtracking (DFS) solution that recursively builds combinations. Alternatively, mention iterative BFS or queue-based approach for comparison.
Write clean code with a mapping array, a recursive helper, and proper base case. Handle empty input and invalid digits gracefully.
State time complexity O(4^n * n) and space O(n) for recursion. Discuss trade-offs: recursion depth vs iterative memory, and potential optimizations like pruning.
Walk through examples like '23' and edge cases like empty string, single digit, and digits with 4 letters (7,9). Verify output correctness.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.